AUSTRALIA's two shiny new F-35 Strike Fighters may never go to war. Needing some 160 modifications to make their model combat worthy, the US Air Force is reportedly considering abandoning those already delivered in favour of new purchases.

Touted by manufacturer Lockheed Martin as the most advanced fighting machines ever built, virtually the entire production run of over 100 machines so far has one glaring problem.

Australia took delivery of two F-35A Lightning II Block 2B aircraft amid much fanfare at the Avalon air show in Victoria earlier this year. Several more are in the late stages of construction, due for delivery next year.

These are almost exactly the same in their specifications to the 108 F-35A Block 2Bs delivered so far to the United States Air Force.

But a controversial development and delivery contract process - known as concurrency - has produced an aircraft with software and components that were never fully tested.

The argument was computer simulation could streamline the whole process, eliminating risk, reducing cost and speeding up delivery.

It didn't.

Now two senior US Pentagon officials responsible for the F-35 program have admitted they are seriously considering abandoning vital upgrades of those aircraft already delivered.

And Australia has at least two Block 2B F-35s that will likely require many millions being sunk into reconstruction and upgrade before they are fully capable of fighting on the front line.

Or they could be restricted to limited training roles, reducing the number of the incredibly expensive aircraft available for active duty.

Or they could be handed to pilots expected to fly into combat with the software and hardware equivalent of one arm tied behind their back.

The Australian ministries of Defence and Defence Industry have been contacted for comment by News Corp Australia. They are yet to respond.

FLYING DUDS

In 2015, the US Director of Operational Test and Evaluation Michael Gilmore wrote testing at that time "did not - and could not - demonstrate that the Block 2B F35B is operationally effective or suitable for use in any type of limited combat operation, or that it is ready for real-world operational deployments".

The consequences of that finding have come home to roost.

"From a production perspective, we have literally 150 to 160 modifications that have to occur on some of our tails to get it to a Block 3 configuration," US Vice Admiral Mat Winter, head of the F-35 Joint Program Office, told the Air Force Association's annual Air, Space and Cyber conference earlier this week.

"Our mods program is almost as exciting and dwarfing our production program."

The Pentagon is considering not modifying all 108 F-35As in its possession to the Block 3F standard. While itself far below advertised F-35 capabilities, the 3F version of the aircraft and its operating system will enable it to carry and use a range of air-to-air and air-to-ground weapons.

The reason given: doing so would be very expensive.

It may be cheaper to just buy new ones off the production line.

"We're looking at a solution space that gives our warfighter options," Admiral Winter said, while admitting his office was expecting a more "logical, more digestible" delivery schedule - meaning further delays.

US Air Force Chief of Staff David Goldfein also admitted at the Air Force Association conference that there was debate within the Pentagon.

"You're going to see us continuing to do a business-case analysis of retrofit of these aircraft," he said earlier this week.

The upshot is dozens of early-delivery US Air Force F-35s are likely to relegated to training duties. They can't use a worthwhile load of missiles or bombs. Nor can they effectively fire their 20mm cannon. And then there is a swath of yet-to-be-addressed safety issues.

BUYER BEWARE

Given those aircraft so far delivered to Australia are essentially the same specification, the Royal Australian Air Force must now either find the money to fix those F-35s it already has - or accept a smaller than expected fighting force than expected.

Exactly how much additional delay these fixes place on the F-35 program is also an issue. The RAAF has already had to buy a handful of F/A-18 Super Hornets to maintain its capabilities while it waits.

It had hoped the F-35A would begin to enter limited service in July 2019, with full operational capability by 2023.

The expanded range of weapons needed for Australian initial operational capability had already been tested, he said.

"The 3F software is being tested quite strongly right now," he told ADM. "That will be delivered in 2018 and we don't go to IOC until the end of 2020, so we've got two years' float and all systems are go."

But that was before the senior US F-35 project commanders began casting doubt on the viability of upgrading existing aircraft to the Block 3F standard.

REJECT SHOP

It's not the first time the defence contract concept of concurrency has failed to deliver.

The predecessor of the F-35, the F-22 Raptor, suffered a similar fate.

Some 30 examples of this ultra-advanced stealth interceptor will never see combat. They've been used only as trainers since production ceased a decade ago because they were not delivered up to expected standards.

This leaves just 150 combat-capable F-22s on active USAF service.

And there is considerable confusion over exactly where the F-35 program stands on actual operational capabilities. The US Marine Corps last year accepting its F-35B jump-jet variants as having met initial operational capability requirements - even though only 89 per cent of the necessary software was delivered, leaving several combat systems inoperable.

Full operational capability is only certified after rigorous and independent testing proves a weapon system can be operated and maintained.

But the US Marine Corps' small fleet of unproven F-35Bs is already serving in Japan and South Korea.

The fix list for problems is extensive.

Many are potentially fatal.

The Pentagon's director of operational testing and evaluation reported earlier this year there were 158 "Category 1" software flaws that could cause death or injury.

Some modifications are as simple as updating the applications on a smart phone. Others need hardware upgrades. Yet more may require extensive rebuilding, such as addressing the vulnerability of its rear engine compartment and tail structure, fixing the pilot's oxygen supply and making the jet's ejection seat safe. And the aircraft isn't allowed to fly anywhere near lightning.

Eight aircraft are currently being assembled as the RAAF's next batch of F-35s. They're due for delivery next year.

Exactly how many of the above problems relate to these airframes is unclear.

PROJECT DELAYS

Lockheed Martin and the USAF made much fanfare about the release of its Block 3 software update earlier this month. But analysts say this ended up being just an interim patch - not the full 3F version promised.

Lockheed Martin has since admitted it has again pushed back the update's release: "We are well positioned to complete air vehicle full 3F and mission systems software development by the end of 2017," a statement reads.

Lockheed Martin ran 46 F-35s off the production lines in 2016. In 2018, it is expected to be in full-swing delivering 130 machines each year. About 900 are due to be delivered over the next five years.

Australia reportedly took delivery of its first two F-35A Block 2Bs for $US94.6 ($A119.5) million each.

Lockheed Martin is boasting it has since reduced the per-aircraft procurement cost of an F-35A to $US85 ($A107.4) million. This may be why the USAF is considering dumping its non-functional examples in favour of fresh copies.

But the price tag does not include the incredible research and development component of the cost - nor the long list of updates, spare parts and man-hours needed to make each one operational.

Australia ordered its first 14 F-35As in November 2009. A second batch was ordered in April 2014 - this time for 58 aircraft. An order for a potential final tranche of 28 is yet to be made.

It may be cheaper to just buy new ones off the production line.

"We're looking at a solution space that gives our warfighter options," Admiral Winter said, while admitting his office was expecting a more "logical, more digestible" delivery schedule - meaning further delays.